Along with a reduction in size, an increase in speed, and weight saving of electronic devices, such as a mobile phone and a personal computer, a capacitor to be used in these electronic devices is required to have a smaller size, a lighter weight, a higher capacitance, and a lower ESR.
A solid electrolytic capacitor is formed of, for example: an aluminum foil or a conductive body (anode body) formed of a sintered body of powder of a metal having a valve action, such as tantalum, niobium, or tungsten, serving as one electrode; a dielectric body layer formed of a metal oxide formed on a surface of the electrode through electrolytic oxidation of a surface layer of the electrode in an electrolyte aqueous solution, such as phosphoric acid; and another electrode (semiconductor layer) formed of a semiconductor layer formed on the dielectric body layer through electrolytic polymerization or the like.
Of the metals having a valve action, an electrolytic capacitor using a sintered body of powder of tungsten as an anode body has an extremely large capacitance change with respect to a DC voltage (bias voltage dependency) as compared to an electrolytic capacitor using an aluminum foil or a sintered body of powder of tantalum or niobium as an anode body, and hence has a problem of a difficulty in its use in a circuit for a precision device, which is required to have a small capacitance change of a capacitor.